1. Field of Invention
The present invention relates to an ink jet printer using hot melt ink. In full detail, it relates to the way in which the printer is constructed to heat a medium onto which images are printed. The invention also relates to a method for preheating a printing medium in a hot melt ink jet printer.
2. Description of Related Art
Conventionally, the recording head used in this type of ink jet printer consisted of a nozzle head with manifold nozzles, an ink melting unit with a heater, and a hopper which holds solid ink pellets. This recording head is mounted on the carriage. When fed, paper is in touch with and supported by the platen provided opposite to the nozzle head. The carriage moves in a direction (of its primary scan) perpendicular to the paper feed direction and by letting hot melt ink liquid gush out from the nozzle head, character or graphic images are printed on the surface of the paper.
In this previous type of ink jet printer, when the hot melt ink liquid adheres to the surface of paper whose temperature is low, the ink immediately solidifies on the surface of the paper. That is, the poor fixing of the ink to the paper causes an event that characters or graphics to be printed are missing, posing a problem that good quality of printed images cannot be assured.
Commonly, the ink jet printer was constructed by installing a heater on the rear side of the platen located opposite to the nozzle head in order to increase the temperature of the paper carried in contact with and supported by the platen. The way in which the printer was constructed allows the temperature of the paper to rise to some level when the hot melt ink adheres to the paper, thus preventing the trouble about the ink fixing to paper.
However, the platen equipped with the heater is positioned to face the nozzle head. This means that paper begins to heat when it comes in contact with the platen. Because there is temperature difference between the paper having arrived at the platen and the heater, the platen must carry the paper at some delayed rate until the paper has heated to the required temperature. Therefore, the printer encountered a problem of low printing speed.
Another problem was that the quality and the properties of paper was affected by the temperature of the platen's heater when set too high to increase the temperature of paper rapidly, leading to the degraded print quality.
The achievement in this invention has been made by the efforts to resolve the problems of the previous ink jet printer.